i think these are easy questions but i just dont get them. really just need help understanding what to do. thanks!

1. the water lily doubles its size every day. from the time it was planted until it completely covered the pond took 26 days. how many days did it take to cover half the pond?
answer is 25 days

I do not know if you need explanation how the answer is 25 or you know it

anyway the answer is 25 as you write the explanation
since the water doubles it size every day and it is need 26 day to fill the pond so the day before 26 , mean day 25 the water will be half of the pond since at the day 26 the water cover the pond and the water double it size every day ..

Work backwards. On the 26 th day the entire pond was covered. Since the lily pad "doubles its size every day", the previous day, the 25 th day, it must have covered 1/2 the pond since "doubling" 1/2 gives 1.